Corrosion of Alumino-Silicate Refractories by Molten Salts: Evaluation and Testing

Abstract

One of the main causes for failure of refractories is corrosion by aggressive liquids or vapours. The intensity and, especially, the extent of this chemical attack greatly depend on the characteristics of the reaction products and the microstructure of the refractory. Any corrosion problem has always two sides to it: (1) the equilibrium state that will be reached sooner or later and (2) how (the mechanism and the rate) is reached. There are several methods, both static and dynamic, to test the corrosion resistance of a refractory material, but none reproduces exactly the actual conditions in a real furnace. They are essencially comparative and a useful tool to assess the mechanism of the corrosion process. In the present work, and in order to keep the number of variables to a minimum, corrosion static finger tests were carried out with comercial alumino-silicate refractories and molten potassium oxide, using nickel crucibles and a vertical kanthal wound furnace. Test temperatures were 900 and 1000° C and test times up to 24h. The weight loss and the change in dimensions of the test pieces were related to the physical characteristics and the microstructure of the refractory through X-ray diffraction and chemical and phase equilibrium analysis, and a mechanism is proposed.